Designs of the above mentioned type are used with purpose to provide such boats with better seaworthiness when the hull is not moving and moving by low speed.
There is a great need for such boats being able to move very fast, being economical as to fuel consumption and furthermore being sea stable. Continuously research and development is going on based on different principles for hull designs, with the purpose of achieving an optimal combination of the above mentioned qualities.
Vessels comprising more than one hull, such as catamaran and trimaran, have great stablilty, but have a hard time running in waves, comprise an expensive structure and also have hulls which are difficult to utilize for many practical purposes.
Hulls having deep V-shaped hull bottoms have good seas properties in the planning condition, but when laying still running at low speed, they have poor stability against heeling,. they easily are influenced by the seaway giving heaving and uneasy movements, and they also have large drift when influenced by wind.
These disadvantags very often are compensated or at least compensation has been tried, by arranging a keel to avoid drifting and to arrange ballast to increase the stability and calmer movements. These means do not correspond with the principles behind a planning hull which as such are light and provide little resistance. The result will be a compromise with corresponding properties and poor fuel economy.
There exists several designs in the field of hulls with water ballast. There are open and closed tanks/tunnels, with without complex regulation and operation mechanisms and finally with different positions and volumes in relation to the hull.
NO 16842 describes a hollow keel which may be filled or emptied for water. The hollow space is situated in the centre plane. To make this boat less exposed to capsizing NO 103 822 describes a hull having only one channel which is closed in the bow and open in the aft to reduce the resistance at running speeds as the water is flowing out of the channel. GB 2 219 973 describes a hull comprising several external, rectilinear channels in the shape of pipes. U.S. Pat. No. 2 892 435 describes a hull having to the centre line symmetricly arranged water tanks which can be filled and emptied individually by means of a compressor.